Conductive compositions have been developed for various purposes including facilitating electrostatic discharge and as a current transfer medium on printed circuit boards. Recently, conductive compositions have been used, instead of conventional conductive wires, as part of electrical systems. In particular, conductive compositions have been used as a means for conducting current from a power source to current operated modules on a variety of objects such as wearing apparel and children's toys.
Examples of desirable electrical systems which use conductive compositions are disclosed in U.S. Pat. No. 5,455,749 which is assigned to the applicant of the present invention and which is incorporated by reference herein. The '749 patent discloses electrical systems which include a power supply, one or more current operated modules and conductive composition for connecting the power supply to the current operated module so that current generated by the power supply can be delivered to the current operating module. In one embodiment, the conductive composition may be colored where the coloring constitutes a substantially nonconductive portion of the conductive composition. In another embodiment, the conductive composition is arranged on an object and forms at least a portion of a design thereon. In another embodiment, the conductive composition includes features which render it sufficiently durable to withstand multiple washes without cracking, substantial resistance build-up or other failure. The aforementioned properties of the conductive compositions disclosed in the '749 patent are desirable in various applications.
Efforts have also been expended to develop conductive compositions which are anistropically electrically conductive. Such anistropic conductive compositions will permit substantial current to flow in the z direction (i.e., normal to the plane of the composition surface), but will prohibit substantial current flow along the x and y directions within the conductive composition (i.e., parallel to the plane of the conductive composition surface). Although this characteristic is desirable, no known anistropic conductive composition includes a pigment. Further, anistropic conductive compositions utilize a single layer composition which includes conductive particles having diameters which vary at different locations within the composition. This features is entirely different from the conductive compositions used in connection with the present invention which will always have at least a first and second layer of different compositions used in combination with each other with the first layer placed on a substrate and a second layer placed on top of the first layer.
U.S. Pat. No. 5,203,975 to Richardson discloses a process for cathodic electrodeposition of a clear coating over a layer of conductive paint. The '975 patent also discloses that multiple layers of conductive composition may be applied to automobile panels and the like. However, the '975 patent does not teach the use of multiple layers of conductive composition in connection with an electrical system. Further, there is no disclosure or teaching in the '975 patent of the concept of applying multiple layers of conductive composition on an object wherein the lower layer includes greater conductivity than an upper layer in order to achieve the concept of "vertical conductivity" which will be discussed in detail hereinbelow.
As used herein, the term substrate includes the surface of any article or object which may be used for consumer or industrial purposes. Further, the substrate may include such articles or objects which have one or more layers of composition applied to the surface thereof beneath the multi-layer conductive composition of the present invention. Examples of such substrates include wearing apparel, toys, furniture, walls, dashboards of automobiles, various electrical, electronic and mechanical devices, etc.
A need has arisen for colored conductive compositions which are available in a wide variety of colors to be used as part of an electrical system on the surface of substrates. For example, it may be desirable to provide a colored conductive composition which has sufficient pigment therein to precisely match the color of an article. It may also be desirable to provide a colored conductive composition which is available in a wide range of vibrant or specific colors.
The prior art has also failed to provide a conductive composition for use as part of an electrical system which is vertically conductive, as defined herein, and which comprises multiple layers wherein the top layer masks one or more lower layers. The present invention addresses the aforementioned shortcomings and needs of the prior art.